Con
Authors: Michael Allon, Michelle L. Robbin
Journal: Journal of the American Society of Nephrology (2008)

In the perfect world, every patient with chronic kidney disease (CKD) would have nephrology follow-up and receive an arteriovenous fistula well before initiating dialysis, every fistula would mature successfully, and, thus, every new hemodialysis patient would have a mature fistula suitable for dialysis. In the real world, many patients with CKD do not have predialysis follow-up by a nephrologist, many fistulas do not mature, and, as a result, many patients start dialysis with a catheter.1 Currently, 75% of incident US patients initiate dialysis with a catheter.2 The conclusion that fistulas are the best type of vascular access is based on the premise that fistulas last longer than grafts and require fewer interventions (angioplasty, thrombectomy, or surgical revision) to maintain their long-term patency for dialysis.3 Careful scrutiny of the studies cited as evidence reveals a strong selection bias. First, many of these studies included only fistulas and grafts that were successfully cannulated for dialysis. Patients whose vascular access failed before it could be used for dialysis (primary failure) were specifically excluded from analysis. Given that primary failures are substantially higher for fistulas (20 to 50%) than for grafts (10 to 20%), their exclusion from the outcome analysis is unfairly biased in favor of fistulas.1 In fact, the comparative studies that included primary failures (intention-to-treat analysis) showed equivalent cumulative survival between fistulas and grafts.4–6 Second, many studies underestimated the true frequency of primary fistula failure by using surrogate outcomes. The “gold standard” for a mature fistula is one that can be cannulated repeatedly with two needles and deliver a dialysis blood flow ≥300 ml/min for at least 1 mo.1 Surrogate fistula outcomes, such as lack of early thrombosis, positive thrill and bruit at the postoperative surgical visit, or ability to use the fistula for just 1 wk, erroneously classify some immature fistulas as being mature, thereby underestimating the true frequency of failure to mature. Third, even fistulas that mature require substantially longer time to successful use than do grafts (approximately 8 to 12 wk for fistulas versus 2 to 4 wk for grafts). This period is further prolonged if the fistula requires a subsequent radiologic or surgical intervention to achieve maturity. For the subset of patients who are already on dialysis at the time of access creation, this translates to prolonged catheter dependence. The proportion of patients dialyzing with fistulas can be (and has been) increased by concerted efforts to encourage early nephrology referral, routine preoperative vascular mapping to increase fistula creation, and efforts to salvage immature fistulas by radiologic or surgical interventions.7 Clinical assessment of fistula maturity should be performed by 6 to 8 wk, and appropriate radiologic or surgical intervention should follow.8,9 Fruitlessly waiting 6 mo before declaring a fistula failure wastes many months that could be used to establish a new, permanent access. Notwithstanding such efforts, several multicenter studies have highlighted important disparities in fistula use among certain dialysis subpopulations. Specifically, a lower prevalence of fistulas has been associated with female gender, black race, older age, obesity, and cardiovascular disease.10 Moreover, these same clinical features have been associated with a higher likelihood of primary fistula failure1 and with delayed transition from a catheter to a permanent access.11 A recent large, multicenter, observational study validated a simple formula for estimation of the risk for primary fistula failure.12 Using four clinical parameters (age, race, coronary artery disease, and peripheral vascular disease), it was possible to stratify the risk for failure to mature. This risk ranged from 24% in patients with scores <2.0 to 70% in those with scores >7.0. Whereas a fistula may be the ideal access choice in a young white man without cardiovascular morbidity, it may be a poor choice in an older black woman with cardiovascular morbidity. In approximately 50% of patients who have CKD and receive their first vascular access, preoperative mapping reveals no suitable vessels for creation of a forearm fistula.1 In such patients, the current Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines recommend placing an upper arm fistula.3 This approach has two drawbacks. First, it sacrifices future options for an ipsilateral forearm access. Why not place a forearm graft first? Second, if the patient is already on dialysis, then it subjects him or her to prolonged catheter dependence. Creating a forearm graft first shortens the period of catheter dependence. Moreover, the forearm graft causes dilation of veins in the upper arm. Thus, when the graft fails, a new upper arm fistula can be created and used much earlier, because vein maturation has already occurred. Certainly, a mature fistula is preferable to a mature graft; however, a mature graft is far preferable to an immature fistula with prolonged catheter dependence. A recent study provided detailed analysis of the tradeoffs between placement of a fistula or a graft.5 As compared with patients receiving a graft, patients receiving a fistula were more likely to have a primary access failure, required more interventions to achieve access maturation, had a substantially longer period of catheter dependence, and experienced more episodes of catheter-related bacteremia. Conversely, among the subset of patients whose access matured, fistulas had superior longevity with a three-fold lower frequency of interventions to maintain long-term patency for dialysis. One size does not fit all. Although fistulas may be the optimal initial vascular access for some patients, grafts may be a better choice for others. One consideration is whether the patient has already initiated dialysis. The patient with CKD may have many months before a mature access becomes necessary. Thus, one has the luxury of placing the fistula and performing subsequent interventions (if needed) to promote maturity. In contrast, prolonged catheter dependence is the tradeoff incurred when fistulas are placed in patients who are already on dialysis. Moreover, the failure rate of fistulas is higher when placed in dialysis patients, as compared with predialysis patients.13 In the United States, the median time from fistula placement to its first cannulation is approximately 3 mo,13 and this is just for patients whose fistula matures. For the substantial group whose fistula fails to mature, a second access must be placed, further prolonging catheter dependence. An unfortunate byproduct of the Fistula First initiative has been the concurrent increase in patients’ undergoing dialysis with catheters. During a 5-yr period in which the proportion of patients who underwent dialysis with fistulas increased by 8% (from 27 to 35%), the proportion of catheter-dependent patients increased by 9% (from 19 to 28%).2 Catheter-dependent patients pay a high price in terms of infection, dialysis adequacy, and mortality. In a recent observational study, bacteremia was observed in 35% of catheter-dependent patients at 3 mo and in 48% at 6 mo.14 Catheter-dependent patients were also three times as likely to have inadequate dialysis, as compared with those who underwent dialysis with a fistula or graft. Moreover, mortality is three-fold higher in patients with catheters, as compared with patients with a permanent access (fistula or graft), and is reduced substantially in catheter-dependent patients who transition to a permanent access.15 The goal of the Fistula First guidelines was to encourage more aggressive efforts to consider fistula placement. Unfortunately, they have been transformed into rigid rules by the dialysis networks and dialysis providers. Medical directors of individual dialysis units now receive regular feedback about the proportion of their patients with fistulas. These reports frequently do not distinguish between mature and immature fistulas. Similarly, surgeons are now judged by what proportion of their vascular accesses placed are fistulas, rather than grafts, without consideration of the primary failure rates. Of even greater concern, Centers for Medicare and Medicaid Services recently proposed a differential reimbursement for outpatient dialysis units on the basis of their proportion of patients with fistulas. Units exceeding the threshold of patients with fistulas would receive higher monthly payments, and those below the threshold would be penalized financially. There is no consideration in these “report cards” of objective differences in primary fistula failure rates among patient subsets. The optimal proportion of fistulas and grafts may well vary among dialysis units, according to their case mix of patients. In summary, the disadvantage of fistulas is their relatively high rate of failure to mature, whereas the major problem with grafts is aggressive neointimal hyperplasia leading to recurrent stenosis and thrombosis, requiring frequent interventions to maintain their patency for dialysis. Fistula placement may be the best option for patients who are not yet on dialysis, whose clinical characteristics predict a relatively low likelihood of nonmaturation, and who have a long life expectancy. Conversely, grafts may be preferred for patients who are already on dialysis, especially if they have already had primary failure of a previous fistula; for patients whose characteristics predict a high likelihood of nonmaturation; for patients with fairly limited life expectancy; and to transition to a future upper arm fistula in patients whose vascular anatomy is unsuitable for a forearm fistula or those with a failed forearm fistula. There is currently intense, ongoing research on pharmacologic interventions to improve fistula outcomes,16 which, if successful, may shift the balance in favor of fistulas. Conversely, pharmacologic interventions that limit neointimal hyperplasia17 may enhance the preference for grafts over fistulas. Ultimately, the decision about which type of vascular access to place in a given patient should consider all of these factors so as to minimize the proportion of catheter-dependent dialysis patients. DISCLOSURES None.